Multiple emulsions are composed of droplets of one liquid dispersed in larger droplets of a second liquid which are then dispersed in a final continuous phase. Generally, the internal droplet phase will be miscible with or identical to the final continuous phase. For example, in a water-in-oil-in-water multiple emulsion W/O/W, the internal and external phases are aqueous.
For a W/O/W system, in which the final continuous phase is aqueous, the primary emulsion is a water-in-oil emulsion W/O, which is then emulsified into the final aqueous phase.
For the purpose of clarity, and in accordance with recognized standards of nomenclature used for W/O/W systems, the aqueous phase of the primary emulsion is designated as W.sub.1, and the primary emulsion is designated as W.sub.1 /O. The primary emulsion W.sub.1 /O includes an oil phase which is designated as O. After the primary emulsion W.sub.1 /O has been further dispersed in the second aqueous phase designated as W.sub.2, the complete multiple emulsion system is designated as W.sub.1 /O/W.sub.2.
According to conventional wisdom, two surfactants or combinations of surfactants must be employed for forming multiple emulsions. One surfactant is used for preparing the primary emulsion W.sub.1 /O, while a second surfactant, generally significantly different from the one surfactant, is used in the final step of emulsification to the W.sub.1 /O/W.sub.2 multiple emulsion. This is for the reason that such multiple emulsion systems involve a great variety of phases and interfaces, and their requirements are such that two stabilizing systems must be employed, i.e., one for each of the oil-water interfaces.
The present invention, in contrast, is a marked departure from such conventional wisdom, and multiple emulsions of the W.sub.1 /O/W.sub.2 type can be prepared using only a single surfactant.